Technical Field
The present invention relates to a light source unit having a plurality of light sources, a lighting apparatus having the light source unit, and an image projection apparatus employing the lighting apparatus.
Background Art
Screen images of personal computers, video images, and image data stored in memory cards can be transmitted to image projection apparatuses known as projectors that can project images onto a screen. Theses image projection apparatuses include a lighting unit using a high-intensity discharge lamp (e.g., super high-pressure mercury lamp) as light source. The discharge lamp can emit high-intensity light with low cost, but needs a given time to stably emit light after turning ON the lamp. In view of such issues of the discharge lamp, as alternative light source of the discharge lamp, a solid light emitting element such as a light emitting diode (LED), a laser diode (LD) of red (R), green (G), and blue (B), or organic electroluminescence (OEL) have been developed as the light source.
By using the solid light emitting element as the light source of projectors, high-speed activation of projectors can be devised, and environmental burden can be reduced. The light source unit using the solid light emitting element may include, for example, a first light source (excitation light source) such as a blue laser diode and fluorescent material, in which a laser beam emitted from the blue laser diode as a excitation light is irradiated to the fluorescent material, with which the fluorescent material is excited to generate light of R, G, B, and the R, G, B light is modulated for gradation for each pixel using a light modulation element such as a digital micro-mirror device (DMD) to generate a color projection image.
In the image projection apparatuses using the laser diode as the light source, how to secure light quantity becomes an important issue, and it has been proposed to arrange a large number of laser diodes in a matrix pattern on a plane or to arrange a large number of laser diodes densely two-dimensionally.
For example, one configuration is disclosed for synthesizing light emitted from a plurality of light sources arranged on a plane with rows and columns, in which a plurality of rectangular reflection mirrors is arranged in a step-like pattern to shorten an interval between light flux emitted from light source in each row, and to shorten an interval between light flux emitted from light source in each column.
If a large number of light sources (e.g. laser diodes) are arranged as laser sources, light emitted from each light source (e.g. laser diode) is required to be focused at a substantially one point in view of compact size of a light-transmission optical system and higher light efficiency.
If a distance from the laser sources (light sources) to a light focus point is set small, a light entering angle at the light focus point becomes greater, and light use efficiency at later optical parts becomes lower and a size of optical system becomes greater.
By contrast, if a distance from the laser sources (light sources) to a light focus point is set great, fluctuation of the light focus point becomes greater due to tolerance of laser, light emitting point and optical system, with which efficient use of light emitted from the light source at later optical parts becomes difficult. This could be solved by increasing a lens diameter, but a greater lens increases the size of optical system
In the above configuration, a cross-section area of light flux is reduced by synthesizing light beams using the reflection mirrors. Because a plurality of reflection mirrors are used to synthesize light beams, setting and adjustment of each mirror is required, and a space for arranging a plurality of reflection mirrors in the step-like pattern is required, with which a compacting of size of light source unit becomes difficult.